1. Field of the Invention
The present invention relates to a display apparatus and a method for driving the same, and more particularly to a display apparatus such as a liquid crystal display apparatus, for example, used for audio visual (AV) equipment, office automation (OA), etc., which uses a voltage generating device forming a part of a driving device and a method for driving the same.
2. Description of the Related Art
FIG. 23 shows an example of the liquid crystal display apparatus as described above. The liquid crystal display apparatus includes a display panel 1001 which performs a display function, a scanning electrode signal driver 1002 for applying a predetermined voltage to scanning electrode lines Y1 to Ym of the display panel 1001 in a line sequence, and a data electrode signal driver 1003 for applying a predetermined voltage to data electrode lines X1 to Xn of the display panel 1001 in accordance with display information. In addition, the apparatus includes a voltage generating section 1006 for generating a voltage applied to the scanning electrode signal driver 1002 and the data electrode signal driver 1003, and a control section 1005 which receives information from an input signal line 1004 to send a control signal to the scanning electrode signal driver 1002, the data electrode signal driver 1003, and the voltage generating section 1006, respectively.
The voltage generating section 1006 includes a data signal voltage generating circuit 1101, a non-selection voltage generating circuit 1102, and a write voltage generating circuit 1103, as shown in FIG. 24.
The voltage generating section 1006 receives a logic circuit power-supply voltage Vcc, a supply voltage Vee, and a control signal Sd. Alternatively, the supply voltage Vee may not be input to the voltage generating section 1006; in such a case, a supply voltage is generated by a booster circuit, etc. in the voltage generating section 1006 based on the logic circuit power-supply voltage Vcc. The voltage generating section 1006 generates a data signal voltage VD, a non-selection voltage VM, a positive electrode side write voltage VH, and a negative electrode side write voltage VL based on input signals such as the logic circuit power-supply voltage Vcc, the supply voltage Vee, and the control signal Sd.
The data signal voltage VD, the non-selection voltage VM, and the write voltages VH and VL satisfy the following Expressions (1) and (2):
VD=2xc3x97VMxe2x80x83xe2x80x83(1)
|VL|=|VH|xe2x88x92|VD|xe2x80x83xe2x80x83(2)
As shown in FIG. 21, the display panel 1101 has a simple matrix type structure in which pixels are arranged in a matrix. Each pixel is composed of one of the scanning electrode lines Y1 to Ym, one of the data electrode lines X1 to Xn, and the liquid crystal 1201 provided between the electrode lines.
Referring back to prior art FIG. 23, the scanning electrode signal driver 1002 is composed of a shift register, an analog switch, etc., and the data electrode signal driver 1003 is composed of a shift register, a latch circuit, an analog switch, etc.
FIG. 25 shows an exemplary operation of the scanning electrode signal driver 1002. It is noted that the scanning electrode signal driver 1002 applies a predetermined voltage to the scanning electrode lines Y1 to Ym in accordance with a latch pulse LP and an alternating signal M.
The scanning electrode signal driver 1002 receives a scanning commencement signal S (not shown), the latch pulse LP, the alternating signal M, and various voltages 1305 (i.e., the write voltages VH and VL, the non-selection voltage VM, and a reference voltage VS) from the control section 1005. The reference voltage VS is generally 0 volt, so that it may be omitted hereinafter. The scanning electrode signal driver 1002 applies the positive electrode side write voltage VH or the negative electrode side write voltage VL supplied from the voltage generating section 1006 to a selected line during a selection period, and the non-selection voltage VM to the selected line during a non-selection period.
Furthermore, FIG. 25 shows waveforms 1306 and 1307 of voltages applied to the scanning electrode lines Yi and Yi+1. As represented by the waveform 1306, during a selection period 1303 in an A frame 1301, the write voltage VH is applied to the scanning electrode line Yi in accordance with the latch pulse LP and the alternating signal M. During a selection period 1304 in a B frame 1302, the write voltage VL is applied to the scanning electrode line Yi in accordance with the latch pulse LP and the alternating signal M, and during a non-selection period, the non-selection voltage VM is applied to the scanning electrode line Yi. On the other hand, as represented by the waveform 1307, during a selection period 1308 in the A frame 1301, the write voltage VL is applied to the scanning electrode line Yi+1 in accordance with the latch pulse LP and the alternating signal M. During a selection period 1309 in the B frame 1302, the write voltage VH is applied to the scanning electrode line Yi+1, and during the non-selection period, the non-selection voltage VM is applied to the scanning electrode line Yi+1 in accordance with the latch pulse LP and the alternating signal M. Herein, the A+B frames each refer to one period of the scanning commencement signal S, and the non-selection period refers to a period obtained by excluding the selection periods from one frame.
FIG. 26 shows signals which are transmitted to the data electrode signal driver 1003. The data electrode signal driver 1003 receives the latch pulse LP, the alternating signal M, a data signal D, and a data transfer clock signal CLK from the control section 1005. Data of each data electrode line Xj is determined based on the data signal D and the data transfer clock signal CLK.
FIG. 27 shows an exemplary operation of the data electrode signal driver 1003. The data electrode signal driver 1003 receives the data signal voltage VD, the non-selection voltage VM, and the reference voltage VS, in addition to the above-mentioned signals, from the voltage generating section 1006.
The data electrode signal driver 1003 applies the latch pulse LP, the alternating signal M, and the data signal transmitted from the control section 1005 and the data signal voltage VD or the reference voltage VS transmitted from the voltage generating section 1006 to a selected line. For example, in the case where data DXj of the data electrode line Xj is at a high level as represented by reference numeral 1509, the data electrode line Xj is supplied with a voltage represented by a waveform 1506 in accordance with the latch pulse LP and the alternating signal M. Reference numeral 1507 shows a waveform of a voltage applied to the scanning electrode line Yi. Thus, a waveform applied to a pixel at a coordinate (Xj, Yi) is as represented by reference numeral 1508.
In a general liquid crystal display apparatus, the data signal voltage VD is constant irrespective of an ambient temperature or the like, as shown in FIG. 27. FIG. 28 shows contrast-supply voltage characteristics at each temperature when the data signal voltage VD is constant.
In FIG. 28, a curve 1603 represents a contrast-supply voltage characteristic at Ta=0xc2x0 C., where Ta is a temperature of a liquid crystal display apparatus; a curve 1602 represents a contrast-supply voltage characteristic at Ta=25xc2x0 C.; and a curve 1601 represents a contrast-supply voltage characteristic at Ta=50xc2x0 C.
As is understood from FIG. 28, if a use temperature of the liquid crystal display apparatus is in a range of 0xc2x0 C. to 50xc2x0 C., it is required to vary a supply voltage for the liquid crystal driving circuit between Va1 and Vc1 in order to improve the contrast of the apparatus. Furthermore, in the case where the temperature dependence of the liquid crystal display apparatus is larger than that shown in FIG. 28, the range of variation of the supply voltage which is a power-supply voltage for a liquid crystal driving circuit is required to be made even larger.
FIG. 29 shows a conventional circuit for generating a power-supply voltage for a liquid crystal driving circuit which is capable of varying a voltage. The voltage generating circuit shown in FIG. 29 includes a variable voltage regulator 1701, resistors 1702 and 1703, a capacitor 1704, electrolytic capacitors 1705 and 1706, and diodes 1707 and 1708.
An input voltage Vin is adjusted by the variable voltage regulator 1701, whereby an adjusted supply voltage Vee is obtained. The input voltage Vin is required to be higher than the supply voltage Vee as a power-supply voltage for a liquid crystal driving circuit. In general, the input voltage Vin is constant.
Thus, in the voltage generating circuit shown in FIG. 29, when an optimum voltage Vc1 of the curve 1603 shown in FIG. 28 becomes high, the input voltage Vin is required to be set to a high value. Consequently, the withstanding voltage of the variable voltage regulator 1701 is required to be set to a high value.
As the potential difference between the optimum voltage Va1 of the curve 1601 and the optimum voltage Vc1 of the curve 1603 becomes larger, the potential difference between the input voltage Vin and the optimum voltage Va1 of the curve 1601 also becomes larger. Therefore, in the case where a general liquid crystal display apparatus is used under the condition of the curve 1601, a power loss of the variable voltage regulator 1701 becomes large. This makes it difficult to minimize the power consumption.
A method for driving a liquid crystal display apparatus according to the present invention including pixels, scanning lines, and data lines, includes the steps of: generating a data signal voltage to be applied to the data lines from a supply voltage; and correcting the supply voltage based on a temperature of the liquid crystal display apparatus.
In one embodiment of the present invention, the step of correcting the supply voltage includes: measuring a temperature of the liquid crystal display apparatus; and correcting the supply voltage so that the data signal voltage becomes lower than a reference voltage in a case where the temperature is higher than a first reference temperature.
In another embodiment of the present invention, the step of correcting the supply voltage includes: measuring a temperature of the liquid crystal display apparatus; and correcting the supply voltage so that the data signal voltage becomes higher than a reference voltage in a case where the temperature is lower than a second reference temperature.
In another embodiment of the present invention, the step of correcting the supply voltage further includes: measuring a temperature of the liquid crystal display apparatus; and correcting the supply voltage to be a first voltage in a case where the temperature is higher than a first reference temperature and correcting the supply voltage to be a second voltage in a case where the temperature is lower than a second reference temperature, wherein the first voltage is lower than the second voltage, and the first reference temperature is higher than the second reference temperature.
A method for driving a liquid crystal display apparatus according to the present invention including pixels, scanning lines, and data lines, includes the steps of: generating a data signal voltage to be applied to the data lines from a power-supply voltage; and correcting the data signal voltage based on a temperature of the liquid crystal display apparatus.
In one embodiment of the present invention, the step of correcting the data signal voltage includes: measuring a temperature of the liquid crystal display apparatus; and correcting the data signal voltage to be lower than a reference voltage in a case where the temperature is higher than a first reference temperature.
In another embodiment of the present invention, the step of correcting the data signal voltage includes: measuring a temperature of the liquid crystal display apparatus; and correcting the data signal voltage to be higher than a reference voltage in a case where the temperature is lower than a second reference temperature.
In another embodiment of the present invention, the step of correcting the data signal voltage further includes: measuring a temperature of the liquid crystal display apparatus; and correcting the data signal voltage to be a first voltage in a case where the temperature is higher than a first reference temperature and correcting the data signal voltage to be a second voltage in a case where the temperature is lower than a second reference temperature, wherein the first voltage is lower than the second voltage, and the first reference temperature is higher than the second reference temperature.
A display apparatus according to the present invention includes: a display panel including a plurality of scanning lines and a plurality of signal lines; a scanning line driver for applying a voltage enabling write signal to the scanning lines in a line sequence; a signal line driver for applying a voltage to the signal lines; a pre-voltage generating device for generating a supply voltage from an input voltage based on a temperature of the display apparatus; and a main voltage generating device for generating a data signal voltage from the supply voltage and outputting the data signal voltage to the signal line driver.
In one embodiment of the present invention, the pre-voltage generating device increases the supply voltage with a decrease in the temperature of the display apparatus and decreases the supply voltage with an increase in the temperature of the display apparatus.
In another embodiment of the present invention, the pre-voltage generating device has a temperature detection circuit for measuring the temperature of the display apparatus.
A display apparatus according to the present invention includes: a display panel including a plurality of scanning lines and a plurality of signal lines; a scanning line driver for applying a voltage enabling write to the scanning lines in line sequence; a signal line driver for applying a voltage to the signal lines; a pre-voltage generating device for generating a supply voltage from a voltage input from outside; and a main voltage generating device for generating a data signal voltage from the supply voltage based on a temperature of the display apparatus and outputting the data signal voltage to the signal line driver.
In one embodiment of the present invention, the main voltage generating apparatus increases the data signal voltage with a decrease in the temperature of the display apparatus and decreases the data signal voltage with an increase in the temperature of the display apparatus.
In another embodiment of the present invention, the main voltage generating device includes a temperature detection circuit for measuring the temperature of the display apparatus.
In another embodiment of the present invention, the main voltage generating device includes a non-selection voltage generating circuit, the non-selection voltage generating circuit has a temperature detection circuit for measuring the temperature of the display apparatus, and the non-selection voltage generating circuit generates a non-selection voltage from the supply voltage as the data signal voltage based on the temperature of the display apparatus.
In another embodiment of the present invention, the non-selection voltage generating circuit increases the non-selection voltage with a decrease in the temperature of the display apparatus and decreases the non-selection voltage with an increase in the temperature of the display apparatus.
In another embodiment of the present invention, the display panel is a simple matrix type display panel.
In another embodiment of the present invention, the display panel is a simple matrix type display panel.
In another embodiment of the present invention, the display panel is an active matrix type display panel.
In another embodiment of the present invention, the display panel is an active matrix type display panel.
Thus, the invention described herein makes possible the advantage of providing a display apparatus in which a variable range of a power-supply voltage can be made narrow, and power consumption can be minimized.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.